id summary reporter owner description type status component version severity resolution keywords cc stage has_patch needs_docs needs_tests needs_better_patch easy ui_ux 28697 Removing unique_together constraint make migration fail with MySQL Esteban C Borsani nobody "I have found Django 1.8.18 fails when removing a model containing a `unique_together` constraint. Django 1.11 works fine. I'm running Python 3.6, mysql 5.7 and using the `mysqlclient` connector. These are actually two errors: * When removing just the constraint, the error is `ValueError: Found wrong number (0) of constraints for myapp_topicpollvote(user_id, choice_id)` * When removing everything altogether the error is `django.db.utils.OperationalError: (1553, ""Cannot drop index 'myapp_topicpollch_poll_id_5bee0f72ec1f3a69_fk_myapp_topicpoll_id': needed in a foreign key constraint"")` Here is the model {{{ # -*- coding: utf-8 -*- from django.db import models from django.conf import settings class TopicPoll(models.Model): """""""""""" class TopicPollChoice(models.Model): poll = models.ForeignKey(TopicPoll, on_delete=models.CASCADE) class TopicPollVote(models.Model): choice = models.ForeignKey(TopicPollChoice, on_delete=models.CASCADE) user = models.ForeignKey(settings.AUTH_USER_MODEL) class Meta: # removing this raises: # ValueError: Found wrong number (0) of constraints for myapp_topicpollvote(user_id, choice_id) # removing all models raises # django.db.utils.OperationalError: (1553, ""Cannot drop index ... unique_together = (('user', 'choice'),) }}} Initial migration: {{{ # -*- coding: utf-8 -*- from __future__ import unicode_literals from django.db import migrations, models from django.conf import settings class Migration(migrations.Migration): dependencies = [ migrations.swappable_dependency(settings.AUTH_USER_MODEL), ] operations = [ migrations.CreateModel( name='TopicPoll', fields=[ ('id', models.AutoField(verbose_name='ID', primary_key=True, serialize=False, auto_created=True)), ], ), migrations.CreateModel( name='TopicPollChoice', fields=[ ('id', models.AutoField(verbose_name='ID', primary_key=True, serialize=False, auto_created=True)), ('poll', models.ForeignKey(to='myapp.TopicPoll')), ], ), migrations.CreateModel( name='TopicPollVote', fields=[ ('id', models.AutoField(verbose_name='ID', primary_key=True, serialize=False, auto_created=True)), ('choice', models.ForeignKey(to='myapp.TopicPollChoice')), ('user', models.ForeignKey(to=settings.AUTH_USER_MODEL)), ], ), migrations.AlterUniqueTogether( name='topicpollvote', unique_together=set([('user', 'choice')]), ), ] }}} Removing just the unique_together: {{{ # -*- coding: utf-8 -*- from __future__ import unicode_literals from django.db import migrations, models class Migration(migrations.Migration): dependencies = [ ('myapp', '0001_initial'), ] operations = [ migrations.AlterUniqueTogether( name='topicpollvote', unique_together=set([]), ), ] }}} Removing everything altogether (unique_together + all models): {{{ # -*- coding: utf-8 -*- from __future__ import unicode_literals from django.db import migrations, models class Migration(migrations.Migration): dependencies = [ ('myapp', '0001_initial'), ] operations = [ migrations.RemoveField( model_name='topicpollchoice', name='poll', ), migrations.AlterUniqueTogether( name='topicpollvote', unique_together=set([]), ), migrations.RemoveField( model_name='topicpollvote', name='choice', ), migrations.RemoveField( model_name='topicpollvote', name='user', ), migrations.DeleteModel( name='TopicPoll', ), migrations.DeleteModel( name='TopicPollChoice', ), migrations.DeleteModel( name='TopicPollVote', ), ] }}} Tracebacks: {{{ Applying myapp.0002_auto_20171011_0311...Traceback (most recent call last): File ""manage.py"", line 10, in execute_from_command_line(sys.argv) File ""/home/esteban/PycharmProjects/venv35/lib64/python3.6/site-packages/django/core/management/__init__.py"", line 354, in execute_from_command_line utility.execute() File ""/home/esteban/PycharmProjects/venv35/lib64/python3.6/site-packages/django/core/management/__init__.py"", line 346, in execute self.fetch_command(subcommand).run_from_argv(self.argv) File ""/home/esteban/PycharmProjects/venv35/lib64/python3.6/site-packages/django/core/management/base.py"", line 394, in run_from_argv self.execute(*args, **cmd_options) File ""/home/esteban/PycharmProjects/venv35/lib64/python3.6/site-packages/django/core/management/base.py"", line 445, in execute output = self.handle(*args, **options) File ""/home/esteban/PycharmProjects/venv35/lib64/python3.6/site-packages/django/core/management/commands/migrate.py"", line 222, in handle executor.migrate(targets, plan, fake=fake, fake_initial=fake_initial) File ""/home/esteban/PycharmProjects/venv35/lib64/python3.6/site-packages/django/db/migrations/executor.py"", line 110, in migrate self.apply_migration(states[migration], migration, fake=fake, fake_initial=fake_initial) File ""/home/esteban/PycharmProjects/venv35/lib64/python3.6/site-packages/django/db/migrations/executor.py"", line 148, in apply_migration state = migration.apply(state, schema_editor) File ""/home/esteban/PycharmProjects/venv35/lib64/python3.6/site-packages/django/db/migrations/migration.py"", line 115, in apply operation.database_forwards(self.app_label, schema_editor, old_state, project_state) File ""/home/esteban/PycharmProjects/venv35/lib64/python3.6/site-packages/django/db/migrations/operations/models.py"", line 359, in database_forwards getattr(new_model._meta, self.option_name, set()), File ""/home/esteban/PycharmProjects/venv35/lib64/python3.6/site-packages/django/db/backends/base/schema.py"", line 320, in alter_unique_together self._delete_composed_index(model, fields, {'unique': True}, self.sql_delete_unique) File ""/home/esteban/PycharmProjects/venv35/lib64/python3.6/site-packages/django/db/backends/mysql/schema.py"", line 80, in _delete_composed_index return super(DatabaseSchemaEditor, self)._delete_composed_index(model, fields, *args) File ""/home/esteban/PycharmProjects/venv35/lib64/python3.6/site-packages/django/db/backends/base/schema.py"", line 349, in _delete_composed_index "", "".join(columns), ValueError: Found wrong number (0) of constraints for myapp_topicpollvote(user_id, choice_id) }}} The other one: {{{ Applying myapp.0002_auto_20171011_0259...Traceback (most recent call last): File ""/home/esteban/PycharmProjects/venv35/lib64/python3.6/site-packages/django/db/backends/utils.py"", line 64, in execute return self.cursor.execute(sql, params) File ""/home/esteban/PycharmProjects/venv35/lib64/python3.6/site-packages/django/db/backends/mysql/base.py"", line 124, in execute return self.cursor.execute(query, args) File ""/home/esteban/PycharmProjects/venv35/lib64/python3.6/site-packages/MySQLdb/cursors.py"", line 250, in execute self.errorhandler(self, exc, value) File ""/home/esteban/PycharmProjects/venv35/lib64/python3.6/site-packages/MySQLdb/connections.py"", line 50, in defaulterrorhandler raise errorvalue File ""/home/esteban/PycharmProjects/venv35/lib64/python3.6/site-packages/MySQLdb/cursors.py"", line 247, in execute res = self._query(query) File ""/home/esteban/PycharmProjects/venv35/lib64/python3.6/site-packages/MySQLdb/cursors.py"", line 411, in _query rowcount = self._do_query(q) File ""/home/esteban/PycharmProjects/venv35/lib64/python3.6/site-packages/MySQLdb/cursors.py"", line 374, in _do_query db.query(q) File ""/home/esteban/PycharmProjects/venv35/lib64/python3.6/site-packages/MySQLdb/connections.py"", line 277, in query _mysql.connection.query(self, query) _mysql_exceptions.OperationalError: (1553, ""Cannot drop index 'myapp_topicpollch_poll_id_5bee0f72ec1f3a69_fk_myapp_topicpoll_id': needed in a foreign key constraint"") }}}" Bug new Migrations 1.8 Normal migrations Unreviewed 0 0 0 0 0 0